1. Field of the Invention
The present invention relates to a sanitary napkin and, more particularly, to a sanitary napkin having a rear portion, which is enhanced in prevention of liquid leakage therefrom and in fitness on the body of a wearer.
2. Description of Related Art
For example, a sanitary napkin, as disclosed in Japanese Unexamined Patent Publication No. 2000-189459, is provided at its longitudinal rear portion with flap portions shaped to bulge laterally from both sides of an absorbent main body. The absorbent main body is provided at its lateral center with an absorbent core, and the flap portions are provided with absorbent cores separate from that in the absorbent main body.
In this sanitary napkin, the menstrual blood having oozed to the rear portion of the absorbent main body corresponding to the buttocks of the wearer""s body can be absorbed by the flap portions. As a result, the sanitary napkin can prevent the sideway leakage of the liquid at its rear portion.
At the rear portion of the sanitary napkin disclosed in the Unexamined Publication, however, the boundary portions between the absorbent core in the absorbent main body and the absorbent cores in the flap portions are given an easily deformable structure. If a twisting force or the like is applied to the rear portion of the sanitary napkin during wear, particularly by the turn-over of a wearer in sleep, therefore, the absorbent core in the absorbent main body is easily deformed at first, and there is a danger of deformation that the flap portions may be slid or folded back toward the center to overlap the central portion.
As the flap portions overlap the liquid receiving side of the central portion, the rear portion is obstructed from absorbing the menstrual blood and allows the sideway leakage. Moreover, the fitness of the sanitary napkin is lost to give an uncomfortable feeling to the buttocks of a wearer.
The present invention has been worked out in view of the shortcoming in the prior art set forth above. It is therefore an object of the present invention to provide a sanitary napkin which is enabled to prevent the sideway leakage from its rear portion effectively without losing the fitness by preventing rear flaps from being deformed toward its central portion while it is worn, particularly in sleep.
According to the invention, there is provided a sanitary napkin having a longitudinal rear portion to be applied to the buttocks of a wearer, comprising:
a longitudinally extending main absorbent region in which a longitudinally extending main absorbent core is disposed between a liquid-impermeable back sheet and a liquid-permeable surface sheet;
side regions positioned on both sides of the main absorbent region; and
boundary regions between the main absorbent region and the side regions, each boundary region being provided with a longitudinally extending leakage-preventing side wall,
wherein in the rear portion, at least a portion of the main absorbent region is formed into a stiff portion having a stiffness higher than that of the remaining portion of the main absorbent region, and in the rear portion, the side regions are protruded laterally to form rear flaps, in each of which an auxiliary absorbent core is disposed between the back sheet and a sheet positioned on a surface side opposite to the back sheet with respect to the auxiliary absorbent core,
wherein in the rear portion, a portion of the main absorbent region having the stiff portion therein, the boundary region and the rear flap have different longitudinal stiffnesses according to the following relationship: the portion of the main absorbent region having the stiff portion therein greater than the boundary region greater than the rear flap.
For example: the portion of the main absorbent region having the stiff portion therein has a stiffness of 9.8 to 29.4 mN; the boundary region has a stiffness of 3.94 to 8.8 mN; and the rear flap has a stiffness of 0.49 to 3.43 mN.
In the rear portion, preferably, the main absorbent core is compressed at least partially to form the stiff portion. More preferably, the main absorbent core is partially compressed in the rear portion so that the stiff portion extends linearly in the longitudinal direction. Alternatively, the main absorbent core, as prepared to be relatively thick in advance, may be substantially entirely compressed at a portion positioned in the rear portion so that the main absorbent core may have a higher stiffness in the rear portion than in a portion forwardly thereof, thereby to provide a stiff portion which coincides with the substantially entire area of a portion of the main absorbent region positioned in the rear portion.
Preferably, each leakage-preventing side wall is folded and secured in the rear portion so as not to allow of rising thereof, but is allowed to rise from the surface side in a portion forwardly of the rear portion.
Preferably, folding portions for facilitating folding of the rear flaps are formed on boundary lines between the boundary regions and the rear flaps. The main absorbent core and the auxiliary absorbent cores may be separated from one another at the folding portions.
Each auxiliary absorbent core may be split into a plurality of segments.
The sanitary napkin of the invention is provided, at its rear portion having the rear flaps, with the stiff portion in the main absorbent region. Therefore, the main absorbent region is hardly deformed when a twisting force acts on the sanitary napkin. On the other hand, the boundary regions between the main absorbent region and the rear flaps are given a bulky structure with the leakage-preventing side walls and a higher stiffness than the rear flaps. When the twisting force acts, therefore, there hardly occurs the deformation in which the rear flaps are folded or slid to overlap the main absorbent region. On the other hand, the rear flaps are easily deformed to fit on the buttocks of a wearer.